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Transcript
Keck Observers' Newsletter, Winter 2010
http://www.keck.hawaii.edu/realpublic/inst/newsletters/Vol8/
Director’s Introduction
Taft Armandroff, Director, WMKO
Welcome to the first Keck Observers’ Newsletter of the new decade.
One of the first astronomy events of the year is the winter meeting
of the American Astronomical Society. Keck Observatory science
results were well represented at the meeting, including special
sessions, media releases, and resulting stories in the national and
international media. I would like to share some of the highlights
with you.
The first announcement was of six new extrasolar planets, five of
which were the first discovered via transit observations from the
Kepler space telescope and then verified and studied in depth with
precision radial velocities from the Keck I telescope and its High Resolution Echelle
Spectrometer (HIRES). The new planets are about the size of Jupiter or larger and tend to
be quite hot. In a separate meeting session, Geoff Marcy, who was involved with the
Kepler findings, and his team, led by Andrew Howard of the University of California,
Berkeley, announced finding the second smallest exoplanet to date. This planet is roughly
four times the mass of Earth and is one of the new class of so-called “super-Earths.” It
was also discovered using Keck I with HIRES.
Another news item was that the Keck telescopes have found evidence of “waltzing black
holes.” Berkeley astronomer Julia Comerford and her colleagues identified 33 dancing
black hole pairs using the Keck II telescope and the Deep Imaging Multi-Object
Spectrograph (DEIMOS). The discovery has profound implications for understanding the
merger history of galaxies, as well as the evolution of supermassive black holes.
Raja GuhaThakurta of the University of California, Santa Cruz, also announced that the
nearest spiral galaxy, Andromeda, has two additional, previously unseen tidal streams of
stars. The findings indicate that M31 has been consuming several neighboring dwarf
galaxies over the last one to two billion years.
Turning from the latest science news to practical matters at Keck Observatory, this
Newsletter contains the latest information that you should be aware of when preparing
your observing proposals for semester 2010B. I particularly draw your attention to the
articles on the LRIS-Red upgrade and on the new laser guide star adaptive optics system
for Keck I. Teams have been working on both of these projects for a number of years to
enable new observing capabilities which exceed any of our “classic” capabilities. The
LRIS-Red upgrade was commissioned successfully in June 2009 and resulted in
dramatically improved performance at far red wavelengths. However, as the article
describes, we have had problems with both of the CCDs since September, and plans are
underway to find a permanent solution. As regards laser guide star adaptive optics on
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Keck I, we are pleased to report that we had first on-sky propagation with the new laser
from Lockheed Martin Coherent Technologies in late January. This is an important
milestone on the road to the commissioning and testing of the new adaptive optics
system. «
Keck I Laser Achieves First On-Sky Propagation
Randy Campbell, Support Astronomer, WMKO
Jason Chin, Senior Electronics Engineer, WMKO
Driven by the high demand for laser guide star adaptive optics (LGS-AO) observing time
on Keck II and our desire to use the LGS-AO system with the Keck Interferometer,
commissioning a laser guide star system on Keck I to provide us with two LGS-enabled
telescopes has been a top priority at Keck for several years. As reported in previous issues
of this newsletter (see Summer 2008 and Summer 2009 issues), the three key goals of
the project are to achieve high reliability via a solid-state laser, to produce a more circular
guide “star” by using a center-mounted laser launch telescope, and to yield a more
visible guide star image with a brighter, more focused beam.
The Keck I laser system was assembled in the labs of Lockheed Martin Coherent
Technologies (LMCT) and passed its acceptance tests in July 2009. The laser arrived at
WMKO headquarters on September 7, 2009 to undergo eight weeks of integration and
testing. The testing phase at HQ was valuable; Keck personnel gained experience and
LMCT personnel furthered the development of this new device during the system’s two
months in Waimea.
This integration and testing phase also allowed us to debug remaining interface,
environmental, and infrastructure issues before taking the system to the summit. Tests at
HQ demonstrated that the new laser has excellent stability once properly aligned at its
operating temperature. As part of the testing, the system ran unattended for over two days
to capture performance data in several key areas: power, spectral content, wavefront
quality, and stability. The laser and remaining subsystems reached the summit on
November 16, 2009. The laser is now installed within the Laser Service Enclosure beside
HIRES on the Keck I right Nasmyth platform. The tweaks and adjustments are of course all
the more difficult in the summit environment, working within the boundaries of an
operational telescope.
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Figure 1. The Keck I laser guide star system employs a center-launched beam
(contrast with the side-mounted design on Keck II) to yield a rounder guide star
image. Photo courtesy Andrew Cooper (WMKO); click to enlarge.
The quasi-continuous wave power output by the laser was measured at 30 W, exceeding
the specification. However, obtaining sufficient power and stability required that LMCT
decrease the temporal pulse width and increase the pulse energy of the laser. This
prevents the full pulse energy from propagating through the fiber due to stimulated
Raman scattering (SRS).
Despite the SRS limitation, the laser and subsystems achieved “first light” on January 28,
2010. The LGS team’s dedicated work over many years culminated in propagating a laser
beam out of the Keck I dome, joining the family of lasers on the Mauna Kea summit (see
Fig. 2). The team is especially proud of having achieved excellent laser performance,
precise alignment of the propagation system, and proper operation of the LGS-AO related
subsystems. Although the on-sky brightness of the laser guide star is currently
insufficient to support science operations, the team will be working in the coming months
to understand the issues and increase the guide star brightness.
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Figure 2. “ First light” with the Keck I laser guide star system was achieved on
January 28, 2010 under full-moon conditions. The Subaru telescope and its laser
are visible in the background, and the Gemini laser can be seen entering the top of
the frame. Photo courtesy Don Holdener (WMKO); click to enlarge.
System testing using the AO engineering camera, SHARC, provided by James Larkin and
Shelley Wright of UCLA, will continue through semester 2010A and into 2010B. The
science operation plan is to move another James Larkin instrument, OSIRIS, from Keck II
to Keck I when the new LGS-AO system is ready. The current plan calls for moving OSIRIS
in mid-December 2010, followed by at least a month of integration and testing before it
returns to science operations. OSIRIS will thus remain available in its current configuration
on Keck II for most of semester 2010B before being removed from service for a few
months. «
The Return of Segment Exchange
Barbara Schaefer, Observing Support Coordinator, WMKO
After completing primary mirror segment recoatings and exchanges in 2005 (Keck II) and
2006 (Keck I), our team discovered cracks in some of the segments (see the Summer
2008 Observers’ Newsletter). Subsequently, we found the cracks to be somewhat more
widespread than originally thought. Accordingly, we suspended segment recoatings and
exchanges in order to study the causes of the cracks, repair the worst of them, and to
prevent additional damage to the mirrors.
In July of 2009 a dedicated outside review team consisting of Maxime Boccas (Optical
Group Leader, Gemini), Peter Gray (Deputy Project Manager, TMT), Jerry Nelson (Keck
Telescope Project Scientist and current TMT Project Scientist, UCSC), and Steve Bauman
(Operations Mechanical Engineering Manager, CFHT) conducted a thorough review of
segment handling procedures with assistance from the internal WMKO review team and
other WMKO specialists. Subsequent to the paper review, we held an on-mountain review,
a dry run with a mock segment, and a continuing review during the first segment
exchange at the end of August 2009. The reviewers made many excellent suggestions
leading to revisions in our procedures. With new procedures in hand and a recently
refurbished aluminizing chamber (see the Summer 2009 Observers’ Newsletter), the
WMKO segment exchange team was ready to embark on recoating and exchanging the
mirror segments in the Keck II telescope. The team still had many things to learn and
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relearn as well as new team members to train. For the first time in several years, segment
exchange was proceeding, but at a slightly slower, more deliberate pace than in past
years.
Quality control is crucial to the coating process. To improve the aluminizing process we
installed a water deionization plant to enable a final, critical rinse of the segments before
coating, and we installed a HEPA filtration system in the coatings lab to significantly
decrease the occurrence of pinholes. These changes enabled the coating team to produce
some of the best coatings seen at Keck in years. The team is now routinely inspecting and
testing all coatings to insure minimum pinholes and maximum adhesion and reflectivity.
The vacuum chamber equipment ensures the coatings are the proper thickness and
evenness.
As of January 2010, 11 of the 36 segments on Keck II have been exchanged, as detailed
in Table 1 and Fig. 3. AO observers have noted the increased reflectivity of the recoated
segments as indicated by the brighter regions on Fig. 4 below.
Dates
Segment Positions
31 August – 1 September, 2009 13, 27
29 – 30 September, 2009
4, 15, 32
28 – 29 October, 2009
24, 25
2 – 3 December, 2009
5, 9, 14, 22
Table 1. Dates of recent Keck II segment exchanges and corresponding segment
positions which were exchanged.
Figure 3. The segment map for Keck II indicates which segments were recoated in
2009. Click image to enlarge.
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Figure 4. Keck II AO wavefront sensor map. Note higher reflectivity of recoated
segments. The segments in this figure are shown at the same orientation as in the
previous figure.
Quantitative measurements and analysis by WMKO Optics Engineer Sergey Panteleev (see
Fig. 5) indicate an increase in reflectivity of 16%–17% on the freshly aluminized segments,
confirming the qualitative visual wavefront sensor evidence.
Figure 5. Relative brightness of primary mirror segments on Keck II measured in
December 2009. Yellow bars indicate improvement over old coating (red). Note
that the relative brightness of the inner ring of segments (segment positions 1–6)
is lower than the others because of partial vignetting by the tertiary tower. Click
image to enlarge.
While plans include completing the exchange of most of the Keck II segments by the end
of August 2010, five segments currently in the telescope should not be handled until our
segment crack repair procedures are in place. We are planning a review of the crack repair
procedures in April 2010 and aim to begin repairs before the end of year. We anticipate
resuming segment exchanges on Keck I shortly after the Keck II exchanges in August. «
OSIRIS Status: Fourth OSIRIS Service is the Charm!
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Jim Lyke, Support Astronomer, WMKO
After a difficult 2009 that saw three servicing missions fail to fix a thermal problem with
OSIRIS, the fourth servicing mission was a success and OSIRIS is again operating
normally. We found the OSIRIS cold head was working at low efficiency due to a poor
thermal contact between the cold head and the internal copper block. During the October
2009 service, we took great care in mating the cold head to the copper block using sheets
of indium. We now have a procedure that will ensure proper thermal connection between
the cold head and the copper block for any future service. We are grateful to OSIRIS PI
James Larkin for his tireless assistance in tracking down and fixing this problem.
The OSIRIS team continues to work on improving the wavelength solution and rectification
matrices needed for the OSIRIS data reduction pipeline. We thank those observers who
dealt with a sub-optimal OSIRIS for their patience as we update the calibrations. Please
continue to check the OSIRIS News Page for updates. «
LRIS Red CCD Charge Transfer Problem Stabilized
Marc Kassis, Support Astronomer, WMKO
In mid-2009, the red arm of our workhorse multi-object spectrometer, LRIS, received a
new dewar with a highly-sensitive detector mosaic that substantially improved the
instrument’s red-side throughput (see the Summer 2009 issue). The CCD array operated
well for several months, but then began deteriorating; images showed pronounced
“smearing” in the serial direction as shown in Fig. 6. This charge-transfer efficiency (CTE)
problem was originally isolated to a single amplifier; however, in the following months a
second and then a third amplifier also began exhibiting the same symptoms, leaving
only one of the original four amplifiers still working well. At present, the only remaining
“good” amplifier is the one on which the longslit spectrum falls in dual-amplifier readout
mode; i.e., the nominal “slitb” position.
Figure 6. Sample LRIS red image showing “ good” area at top and “ bad” area at
bottom. Note the vertical “ smearing” of cosmic rays in the affected region, as
highlighted in the inset. The amount of signal lost in the smearing may be as much
as 20% of the total light. Click image to enlarge.
Based on extensive thermal modeling of the CCD package design, UCO/Lick staff
concluded that thermal cycling of the CCDs might have caused the CTE problem. Thermal
cycling occurs when LRIS is installed or removed from the telescope as part of the
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observatory’s regular instrument switching procedures. When we turn power to LRIS off
during the normal instrument changeout process, the dewar temperature monitoring
system stops, causing the CCD temperature to drop from an operating temperature of
-140 C to as low as liquid nitrogen temperatures (-196 C). The new Lick thermal models
suggest that excessive mechanical stress may occur if the LRIS-R mosaic gets colder than
-150 C.
To stabilize the CCD temperature, WMKO and UCO/Lick staff have added new electronics
to LRIS to maintain power during instrument changeouts and new software that will supply
a steady heater current, ensuring that the CCD temperature remains at or above the
operating temperature during this process. With these additions in place, we hope to
maintain the current operational state of the LRIS red CCDs; however, this will not recover
the three degraded amplifiers, which remain unusable for science. Before using LRIS,
observers should review the LRIS news to check whether these stabilizing measures have
been successful.
To take advantage of the one remaining good amplifier, observers acquiring data in
longslit mode should select dual-amp readout mode to save readout time. Observers
acquiring imaging or multislit data should select single-amp readout mode with the
right-side amplifiers to obtain good images over 1/2 of the mosaic at the expense of
doubling the readout time to 3 minutes per exposure. We have updated the Xpose GUI for
the red side to include the option of reading out the mosaic in single-amp mode using
the right-side amplifiers. Staff from UCO/Lick Observatory have updated the ds9 image
display tool so that it will display images in the same orientation regardless of the readout
mode.
Observers planning to use slitmasks must design their masks to place slits on the “good”
region on the red side. This example Autoslit slitmask design shows where slits may be
placed to land on the “good” side, which is opposite to the side with pickoff mirrors when
in use. Highest-priority objects for red-side observations should be placed on the “good”
side, but slits for blue-side science may be placed anywhere on the slitmask.
Longer term, we intend to identify replacements for the current LRIS red CCDs with
assistance from UCO/Lick staff; options include both 2K × 4K and 4K × 4K devices. The
UCO/Lick detector team is currently characterizing candidate 2K × 4K CCDs which have a
different packaging than the devices currently in use with LRIS. The second replacement
option is a monolithic LBNL 4K × 4K detector, which would also represent an upgrade to
the current mosaic. «
Integral Field Spectroscopy Comes to ESI
Gregory D. Wirth, Support Astronomer, WMKO
The ESI Integral Field Unit (IFU) has completed its commissioning phase, providing a new
ESI observing mode which offers medium-resolution spectroscopy for extended targets.
Developed at UCO/Lick by Andy Sheinis and Joe Miller, the unit employs an image slicer
arrangement to reimage a contiguous 4.0 × 5.7 arcsec field of view into 5 separate spectra
covering 20 arcsec of slit length with a slit width of 1.13 arcsec. The resulting
echellette-mode spectra cover the normal ESI wavelength range of 0.37–1.0µm at a
resolution of R=3500.
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Figure 7. Left: Simulation of a possible target for the ESI Integral Field Unit (IFU), a
galaxy much wider than the typical ESI slit. The red boxes indicate the 5 slitlets in
the IFU. Right: Small section of the corresponding ESI spectrum consisting of 5
individual spectra corresponding to the 5 slitlets in the IFU.
Throughput for the unit itself is only 45%–55%, reducing the advantage of the greater field
of view, but for certain programs this new capability for ESI may yield greater observing
efficiency. For further information on the IFU, please refer to the ESI IFU documentation
and the corresponding astro-ph article by Andrew Sheinis. If you plan to use the IFU for
an upcoming ESI run, please contact your support astronomer in advance. «
Keck Interferometer Offers Improved Performance and New ASTRA Mode
Sam Ragland, Interferometer Operations Manager, WMKO
Julien Woillez, Interferometer Scientist, WMKO
The Keck Interferometer (KI) combines the two Keck telescopes as a long baseline
interferometer, providing several high-angular-resolution observing modes in the nearand mid-infrared. KI has been used to study a variety of scientific phenomena including
young stellar object disks, young binary stars, debris disks, and active galactic nuclei
(AGN). About seven KI science nights are awarded each semester through the various time
allocation committees. The H- and K-band visibility amplitude modes, the most sensitive
in the world, have been offered for several years now. The Keck Interferometer team has
recently improved the performance of angle tracking in the H-band, enabling K-band
interferometric observations of a sample of bright AGN for the first time as reported in a
recent article by Kishimoto et al.
The nuller instrument, operating in the mid-infrared, continues to be available for science
in 2010B but future availability will be determined on a semester-by-semester basis. The
high-spectral-resolution mode (V2-SPR), offered for shared-risk science during
previous semesters, will transition into a facility-class capability in semester 2010B. The
L-band (V2-L) and simultaneous K/L (V2-DFPR) visibility modes continue to be available
for shared-risk observing in 2010B.
On the ASTRA project front, the 2009B semester was dedicated to commissioning the
dual-field subsystems located at the focus of the Keck I and Keck II adaptive optics
modules. These systems are responsible for selecting a bright reference object up to
30 arcsec away from a faint object of interest in order to perform an observation similar to
natural guide star AO. The interferometer team achieved first fringes on a bright star pair
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three days before the new year. We hope to obtain the first faint phase-referenced
observations in the 2010A semester with the expectation of reaching a K-band magnitude
of at least 13. Development of the astrometric mode continues and we aim to complete the
first astrometric engineering nights this summer.
All Keck users are eligible to propose for science-observations with the Keck
Interferometer. Observations are currently taken in service observing mode and may be
scheduled in campaign mode. More details of KI sensitivity and observing parameters
may be found on the NExScI web pages. «
Novel Techniques Developed for Adaptive Optics
Al Conrad, Support Astronomer, WMKO
Jim Lyke, Support Astronomer, WMKO
Several exciting studies carried out recently with adaptive optics (AO) have motivated
WMKO support astronomers and engineers to develop new capabilities for that system.
These new observing modes may be applicable beyond the specific program for which we
developed them; for example, expanded wavelength coverage for NIRSPAO, motivated by
a project to study methane on Mars, will permit high-spatial-resolution spectroscopy of
targets in the infrared K, L and M bands.
Differential Tracking
Since its inception, a key limitation of the Keck II laser guide star (LGS) system for
studying solar system targets has been the need for the tip-tilt reference object (whether a
star or a moon) to be moving at the same rate as the target. Thanks to a recent software
upgrade, the system can now accommodate differential motion between the science target
and its tip-tilt reference beacon, allowing us to use AO on moving objects. This mode has
been applied both in regimes with strong scattered light (e.g., Jupiter and Mars) and for
programs where scattered light is not a factor (e.g., Kuiper belt objects).
For Jupiter and Mars, scattered light presents a challenge. For these programs, the tip-tilt
reference (moon or appulse star) must be approximately 10th magnitude or brighter. On
the other hand, KBO studies have shown that the LGS differential tracking mode can be
used for programs unaffected by scattered light with no restrictions beyond the standard
specifications for LGS-AO guide stars (for example, R < 18).
Use of the LGS-AO differential tracking mode could be expanded to other programs. For
example, faint asteroids in the main belt, and in the Greek and Trojan swarms at the
Jovian L4 and L5 points, frequently pass close to stars brighter than 18th magnitude. In
these cases, that star could be used together with LGS-AO differential tracking to acquire
diffraction-limited images of these objects, enabling searches for companions and/or
studies of the physical properties of the asteroids themselves.
NIRSPAO Thermal-IR Capability
NIRSPAO is a NIRSPEC-behind-AO mode that can be used to obtain high-resolution
spectra at diffraction-limited spatial resolution. A long-standing restriction has prevented
the use of NIRSPAO at longer wavelengths. The special pupil stop needed for NIRSPEC to
work behind AO resided only in the same wheel as the K-, L-, and M-band filters. Until
recently, no AO pupil stop existed in the second filter wheel.
During September 2009, a team led by NIRSPEC Instrument Master Jim Lyke successfully
installed this second pupil stop during a servicing mission on the warm dewar. NIRSPAO
has since been used to study Mars in the K and L bands with the AO system (in NGS
mode) locked onto features on the Martian surface, initiating a new era of high-resolution
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infrared spectroscopy of solar system targets.
Figure 8. The authors used NIRC2 to image Mars in June 2009 with the Keck II
Adaptive Optics system, achieving an angular resolution unprecedented in
ground-based astronomy. After processing to improve sharpness, the images
easily reveal individual features including Schiaparelli crater. These observations
took place during a rare opportunity when Mars was small enough (in apparent
size) to observe with the AO system. With the new differential-tracking capability
for the LGS-AO system, observations of even greater clarity will be possible
whenever Mars is close enough to a star which can be used for tip/tilt reference.
As an example of the spatial resolution achievable on the Martian surface with Keck AO,
Fig. 8 shows NIRC2 data collected during June 2009. At this time, Mars subtended
4.7 arcsec and could thus be observed directly with AO in NGS mode. Note that features as
small as Schiaparelli crater are easily resolved in these images, making these the highestresolution ground-based images of Mars ever acquired.
This new capability for NIRSPAO could prove useful for other programs; for example,
NIRSPAO may now be capable of resolving emission from CO, or volatiles such as
ammonia and methane, within circumstellar disks well enough to determine their location
within the disk. However, observers considering such applications should be aware that
the background flux in NIRSPAO mode is almost five times higher than for NIRSPEC
without AO due to the additional “warm” surfaces in the optical path. Please refer to the
NIRSPEC web pages for further information. «
Operations Notebook
Robert Goodrich, Observing Support Manager, WMKO
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The WMKO operations team continues to make behind-the-scenes changes to promote
efficiency at the observatory. In some cases, these changes should lead to subtle
improvements in the observing experience. For example, the Instrument Preventative and
Predictive Maintenance (IPM) team has reported finding nearly fifty incipient problems as
they perform new PM tasks on various instruments. Presumably, some of these problems
would have led to failures on sky and subsequent loss of observing time had the team
not found and fixed them. Other changes, such as reducing our Night Attendant (NA)
hours, can make troubleshooting a subset of night-time problems less efficient.
Determining whether the likelihood of such problems outweighs the cost of the
corresponding preventive measures is our continuing challenge.
The NAs have also taken on the important task of watching for aircraft during LGS-AO
operations to prevent our laser from inadvertently illuminating a plane. This task involves
spending long hours outside in the cold, continuously scanning the sky, and we salute
our hardworking NA crew — Scotty Paiva, Sniffen Joseph, Nick Jordan, and Douglas
Macilroy — for performing this job. Several members of our operations staff, including
Steve Shimko, Dennis Callan, Jamie Higginson, and Kirk Tateishi, are working with the
NAs to make this task more comfortable by designing wind breaks and procuring
appropriate cold weather gear.
Figure 9. Estimated V-band seeing vs. time as measured by the new MASS/DIMM
unit installed on Mauna Kea. The DIMM values (red dots) are the better predictor of
telescope seeing since they reflect ground-level conditions.
In a welcome development, real-time data on Mauna Kea weather and seeing conditions
are now available on the Mauna Kea Weather Center (MKWC) website thanks to a
MASS/DIMM instrument loaned by the TMT project. The equipment consists of a MultiAperture Scintillation Sensor (MASS), sensitive to atmospheric turbulence above 500 m,
and a Differential Image Motion Monitor (DIMM), measuring the ground layer below
500 m. CFHT houses the instruments on its summit weather tower, maintains the
instrumentation, and provides a low-level interface, while MKWC provides the high-level
interface. An example of the MKWC graphic from January 12–13, 2010 is shown in Fig. 9.
Note that the DIMM data are more relevant to telescope seeing. Raw data can be
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downloaded using the links in the section labeled “Last Seeing Data” on the MKWC
website. «
UCO/Lick Seeks Input on Next-Generation Slitmask Tools
Steve Allen, Programmer/Analyst, UCO/Lick
The software which Keck observers currently use to design and submit LRIS and DEIMOS
slitmasks is based on technologies over a decade old. The Scientific Programming Group
at UCO/Lick is starting to plan how observers will create and submit slitmask designs for
use with the next generation of slitmask-enabled instruments and solicits advice from the
WMKO observer community to assist in the design process. If you would like to offer your
input, please take a few minutes to complete our online slitmask survey at
http://spg.ucolick.org/cgi-bin/Masks/slitmasksurvey.cgi. Many thanks in advance for
your suggestions and comments. «
Espresso Returns to Keck
Jim Lyke, Support Astronomer, WMKO
After a long hiatus, observers may once again treat themselves to
a great cup of coffee while observing! We have purchased a small
espresso machine and installed it in the kitchen/lounge in the
wing adjacent to the remote observing rooms. The Espressione
Café Retro is easy to use and produces a great cup of coffee.
Instructions are provided on the machine; coffee, milk, and barista
not included. «
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